| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 4554368 | Environmental and Experimental Botany | 2014 | 10 Pages |
•With a KM value of 26 μM poplar PttNRT2.4 is a high affinity nitrate importer.•PttNRT2.4 expression is nitrate induced in root hairs of non-mycorrhizal poplars and ectomycorrhizas.•Nitrate-based PttNRT2.4 induction in mycorrhizas point toward nitrate diffusion through the fungal mantle.•As result, soil nitrate is taken up by mycorrhized host plants as extra nitrogen source in presence of reduced nitrogen.
As a result of natural or artificial disturbances, elevated nitrate concentrations are found in forest soils and could thus be important for tree nutrition. In an EST project of Populus tremula × tremuloides/Amanita muscaria ectomycorrhizas three putative high-affinity nitrate transporters of the NRT2 gene family were discovered of which PttNRT2.4A and PttNRT2.5B were expressed highest in fine roots at comparable levels.Ectomycorrhiza formation resulted in a nitrate independent enhanced PttNRT2.5B gene expression. However, as characterization of transport properties by heterologous expression failed, PttNRT2.5B function still remains unclear.With a KM value of about 26 μM, as determined by heterologous expression in Xenopus laevis oocytes, PttNRT2.4A is a high affinity nitrate importer. In fine roots of nitrate depleted poplar plants PttNRT2.4A expression was very low. Transcript levels increased 75-fold when plants were exposed to low nitrate concentrations (10–100 μM). This increase was lower at elevated nitrate concentrations or in the presence of ammonium. By generating P. tremula × tremuloides plants transformed with a PttNRT2.4A promoter GFP fusion construct, nitrate induced PttNRT2.4A expression was localized in root hairs but not in underlying cortex cells.In ectomycorrhizas of ammonium grown plants PttNRT2.4A expression decreased compared to non-mycorrhizal fine roots. However, nitrate induced PttNRT2.4A expression in ectomycorrhizas indicates nitrate permeability of the fungal mantle under certain conditions.
